Welding properties of high strength steel for coal mine hydraulic support
In order to realize the high quality welding of Q550D high-strength mid-thick plate,and promote its popu-larization and application in the field of coal mine hydraulic support.The welding test of 550 MPa high-strength mid-thick plate for coal mine hydraulic support was carried out by CO2 semi-automatic gas-shielded arc welding.The mi-crostructure of welded joint was observed by optical microscope.The crystallographic characteristics and fine mor-phology of coarse-grained heat-affected zone in welded joint were observed by electron backscattered diffraction and transmission electron microscope.The comprehensive mechanical properties of the welded joint were measured by tensile and impact testing machines.The results showed that the yield strength and tensile strength of the welded joint are 655 MPa and 747 MPa,respectively.The elongation is 18.5％,and the fracture occurs at base metal.The impact energy of weld metal,fusion line,fusion line outward 1 mm,fusion line outward 3 mm and fusion line outward 5 mm at-20 ℃ are 82,113,106,124 and 159 J,respectively.The average hardness of weld metal,coarse-grained heat-affected zone,fine-grained heat-affected zone,intercritical heat-affected zone and base metal are 294.07HV,293.18HV,264.67HV,275.02HV and 278.49HV,respectively.Compared with the base metal,the weld metal and coarse-grained heat-affected zone are local hardening zone with hardening rates of 5.59％and 5.27％,respectively.And the fine-grained heat-affected zone and intercritical heat-affected zone are local softening zone with softening rates of 4.96％and 1.25％,respectively.The acicular ferrites with high dislocation density crisscross and bite each other,which can effectively prevent crack propagation and improve the mechanical properties of the coarse-grained heat-affected zone.The large angle boundary ratio of granular bainite,strip bainite and acicular ferrite generated within the parent austenite grain in the coarse-grained heat-affected zone is 72.12％,and the average equivalent sub-grain size is 1.28 μm.High proportion of large-angle grain boundaries and equivalent sub-grains with small size can effectively resist crack propagation,which is the main reason for the excellent low-temperature impact toughness of the welded joint.
NETL
NSTL
万方数据
